If a turn signal in a motor vehicle malfunctions, the malfunction must be detected and the driver of the motor vehicle must be notified. Older model turn signal systems use a single incandescent turn signal bulb on each side in the front of the vehicle and a single incandescent bulb on each side in the rear of the vehicle. The two bulbs, one front and one rear, are wired in parallel and each might draw as much as one ampere of current. If either bulb fails, usually as an open circuit, failure detection is relatively easy because of the large resulting change in the current supplied by the turn signal power supply. The resulting change in current can be detected, for example, as a change in the voltage drop across a resistor in series between the power supply and the two bulbs. Upon detection of a large change in the current from the turn signal power supply the driver of the motor vehicle can be alerted, for example, by causing the remaining turn signal and the dash board turn signal indicator to flash at an increased rate. The series resistor and the circuit for detecting the failure can be located in or near the dash board area of the motor vehicle in close proximity to circuitry needed to alert the driver.
The rear turn signal element in newer model motor vehicles turn signal systems can be a plurality of light emitting diodes (LEDs) instead of an incandescent bulb. The LEDs are usually arranged as a plurality of parallel banks of series connected LEDs. Individually each LED draws only a few tens of milliamps of current when operating. A failure of a single LED or even of a bank of LEDs causes only a small change in the total turn signal current. Failure of an LED in a rear turn signal element is difficult to detect by detection circuitry located in or near the dash board where the malfunction alert circuitry is located. Failure of a single LED or a small bank of LEDs causes such a small change in the total turn signal current that the change may be masked, for example, by noise on the power line extending from the rear of the motor vehicle to the dash board area. It has thus been common to place malfunction detection circuitry near the rear turn signal element where accurate detection of LED failure can be insured. A failure signal from the detection circuitry must then be transmitted to the malfunction alert circuitry over an error wire that runs from each rear turn signal assembly to the dash board. The extra error wires (one for each side of the vehicle) add to the cost of the motor vehicle and are a potential source of an additional failure mechanism.
Accordingly, it is desirable to provide a method for reliably and inexpensively detecting the failure of a light emitting diode in a motor vehicle turn signal assembly. In addition, it is desirable to provide a motor vehicle turn signal assembly that can detect malfunctioning of an LED in the assembly without additional wiring extending from the assembly to the dash board area. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.